1. Field of the Invention
This present invention relates to the field of energy recovery systems, program product, and related methods.
2. Description of the Related Art
Many different types of processes consume multiple steam levels and electricity to obtain an output result, or to produce a required product or compound. For large-scale processes that, for example, consume significant amounts of fuel and steam, it is preferable to optimize the consumption of energy through careful operation, design or reconfiguration of the plant and the equipment used. Further, in some industrial manufacturing processes, specific streams of material flows need to be supplied to different types of equipment and machinery at specific temperatures. These material flows may need to be heated or cooled from an original starting or supply temperature to a target temperature. This, in turn, requires the consumption of steam to heat specific streams and consumption of water, for example, to cool down specific streams.
The total energy employed or consumed by the industrial manufacturing processes can be optimized to a global minimal level, for example, through careful placement and configuration of specific material streams with respect to one another. There may be, for example, the potential for hot streams that require cooling to be placed in proximity with cold streams that require heating. Streams having thermal energy already present that need to be removed (waste heat) or streams that need to have heat added can be associated with one another to optimize the energy consumption of the process. A network of heat exchangers can be synthesized to provide a medium for utilizing this waste heat to provide heat to those streams that need to have heat added. This heat exchanger network can be a very important sub-system in any new plant.
As such, the heat exchanger network synthesis problem has arguably been one of the most studied problems in the field of process synthesis in the last four decades. The systematic synthesis of heat exchangers network, however, has proven to be a challenging task. During the last three decades a considerable number of methods have been proposed and utilized in commercial software and/or academia. These methods are referenced in the two famous review papers of T. Gundersen and L. Naess, “The Synthesis of Cost Optimal Heat Exchanger Networks,” Computers and Chemical Engineering, vol. 12, pp. 503-530 (1988), and of Kevin C. Furman and Nikolaos V. Sahinidis, “A Critical Review and Annotated Bibliography for Heat Exchanger Network Synthesis in the 20th Century,” Industrial Engineering & Chemistry Research vol. 41, pp. 2335-2370 (2002).
The state-of-the-art software widely used in industry for initial synthesis of the heat exchange network (HEN) includes, for example, an AspenTech Inc. product known as Aspen Pinch, a Hyprotech Inc. product known as HX-NET (acquired by AspenTech), a KBC product known as Pinch Express, and a UMIST product known as Sprint, which attempt to address the heat exchanger network synthesis problem using the well known pinch design method, followed by an optimization capability that optimizes the initial design created by the pinch design method through use of streams split flows in streams branches and manipulates heat exchanger duty by utilizing the global network heat recovery minimum approach temperature as an optimization variable, in a non-linear program to recover more waste heat, shift loads among heat exchangers to remove small units, redistribute the load (duty) among units, and optimize surface area, of course, always within the constraints of the topology determined using the pinch design method. The pinch design method, followed by the optimization capability method, or combination of methods, has seen wide spread acceptance in the industrial community due to its non-black box approach. That is, the process engineer is in the feedback loop of the design of the heat exchangers network such that the process engineer can make design decisions that can change with the progress of the design. Recognized by the inventors, however, is that in all applications of near pinch and multiple pinches problems to the above software applications, their respective calculations render a larger than optimal number of heat exchange units. Also recognized is that, in addition, software applications that use the pinch design method or that use the pinch design method as a basis for its initial design followed by the optimization option for branches and duties can not handle certain situations/constraints/opportunities that can render better economics, for example, from energy, capital, or both points of view, which means that some superior network designs will never be synthesized using such applications.
Other methodologies include mathematical programming-based methods. Although such methods have been in academia since the late eighties, they are still not widely used on a large scale in industrial applications for several reasons. For example, the computational requirements of such methods are substantial, especially for large problems, and the resultant solution, in general, can not guarantee globality. Additionally, besides the inherent disadvantage of the black box nature of such methods, the mathematical programming-based methods require assumptions regarding problem economics, the types of heat exchangers used in the network (shell & tube, twisted tube, plate and frame types, etc.), the need to know the several utilities types and temperatures beforehand, and the non-inclusive nature of the “transshipment model” used for streams matching and superstructure application, which explains why the pinch design method is still the leading method in industry, even with its inadequacies.
It has been recognized that heat exchanger network synthesis of both switchable and flexible heat exchanger networks under variations in process conditions, however, is more difficult than the nominal design. Nevertheless, although literature has been in existence since the late eighties which has identified a desire for flexibility in the heat exchanger network design, apart from the stochastic methods (trial and error approach) which also require unrealistic assumptions and which are very difficult to implement by regular process engineers, there still only remains the pinch-based approach and the mathematical programming-based methods.
As introduced above, the pinch-based approach remains the industry practice even though it is in-systematic and needs iteration without guarantee to reach, at the end, a feasible and cost effective design. In brief, the pinch-based approach uses the pinch design method as a basis to develop a heat exchanger network that can handle process variations. It sets up multiple operating cases in a step which is in-systematic and ad hoc. It then uses the pinch method to design individual networks for each case. It then tries to merge the individual designs to form a final one. Thereafter, it uses the disturbance and uncertainty scheme to test for feasibility of the network in the face of the disturbances and uncertainty. If the network is not feasible, it again in-systematically adds contingencies to try to make it feasible. If still not feasible, the approach sets new multiple operating cases and repeats the procedures iteratively. If the new loop renders a feasible network, optimize the network and recheck for feasibility. Again, if infeasibility arises, the problem is not solved and iteration in-systematically provides the only solution. Nevertheless, as noted above, even with the requirement for a substantial amount of ad hoc decisions and iteration, the pinch-based approach is still leading in most commercial software.
On the other hand, heat exchanger network synthesis under varying conditions for switchability and flexibility using mathematical programming is even more difficult to use and inherently has myopic assumptions. For example, the mathematical programming approach can be extremely difficult because the nominal design one-period problem itself is difficult to employ to try to solve industrial scale problems without extensively applying simplifying assumptions in the type of heat exchangers used, places of the service units, number of streams matching more than once, etc. As such, it is expected that applying such approach to a multi-period synthesis problem would be extremely difficult. It may be particularly difficult to implement, for example, because from industry point of view, the basic assumption regarding the disturbances and uncertainty schemes that define exactly each operating period at the design phase, is completely unrealistic.
Accordingly, recognized by the inventors is the need for an improved system, program product, method or technique that can address any or all of the above optimization issues, particularly during the design stage, and which can minimize energy and capital costs for waste heat recovery through application of a systematic process prior to the actual design, construction or modification of actual plant and equipment. Particularly, recognized is the need for a systematic heat exchanger network synthesis method with life-cycle switchability and flexibility under all possible anticipated combinations process variations that exhibits much better capabilities than the ad hoc in-systematic pinch approach and that can render in all cases, a network design including a number of the exchanger units that is less than or an equal to the number of heat exchanger units for the networks synthesized using the pinch design method, even when combined with heat exchanger duty and branch optimization options currently implemented in commercial software, for all types of problems to include pinched problems, problems with near pinch applications, as well as multiple pinches problems, that need both heating and cooling utilities, and problems that need only cooling or only heating utility (called threshold problems).
Also, recognized by the inventors is the need for improved methods, systems, and techniques that can address cases where the optimal solutions can be provided by matching a hot stream with a hot stream or a cold stream with a cold streams, or partially converting a hot stream to a cold stream or a cold stream to a hot stream. Further, recognized by the inventors is the need for improved methods, systems, and techniques which can provide a guarantee of feasibility under a given realistic disturbance scheme, which can produce heat exchangers networks within the optimal number of units, which addresses life cycle switchability and flexibility, and which can be used to calculate optimal target temperatures for streams within a realistic operating window range at the design phase under all possible combinations of anticipated disturbances and uncertainty.
It is further recognized by the inventors that it would be beneficial if the heat exchanger network design, according to such methods, systems, and program product, were also such that the network was configured to be “easily-retrofitable” in future times to allow for growth and/or for contingencies such as, for example, those due to dramatic changes in energy prices resulting in a need to operate under future time-dependent operating modes, disturbances and uncertainty schemes. Notably, it is not believed that the pinch design method could adopt retrofitability during the design stage as it does not have a systematic method to select an optimal set of supply temperatures, target temperatures, and/or stream specific minimum temperature, either in general, or based upon a trade-off between capital and energy costs, in particular, and because its pinch design philosophy starts the design of the network only after selecting an optimal initial conditions including supply temperatures, target temperatures, and network global minimum approach temperature using, for example, the “SUPERTARGET” method which targets for both energy consumption and the heat exchanger network area at the same time. Even by repeating such sequential philosophy using different ranges of supply and/or target temperature values, the resulting new network structure would not be expected to consistently resemble the previous network structure, in class, and thus, would result in a requirement for an undue expenditure in network reconciliation efforts, to try to form a continuum of common-structure heat exchanger network designs which can be used to facilitate user selection of a physical heat exchanger network structure satisfying both current user-selected economic criteria and anticipated potential future retrofit requirements and corresponding physical heat exchanger network development and facility surface area of allotment based upon such selected design.